There is a real need for the efficient production of hydrogen for use as a fuel in both vehicular and stationary engines and fuel cell systems. While hydrogen is a clean and efficient fuel for such energy producing systems, it is both expensive to produce in a pure form and unsafe to store in quantity (because of its combustibility). Moreover, hydrogen is expensive and heavy when stored in containers of practical size.
Fossil fuels or their derivatives, such as natural gas or methanol, are currently converted to hydrogen for use in a fuel cell by means of a complicated set of bulky components: a reformer (to convert the fossil fuel to a mixture of hydrogen, carbon dioxide, carbon monoxide and water vapor); a shift converter (to remove most but not all of the carbon monoxide); and one or more gas purifiers (needed if the hydrogen is to be used in a proton-exchange membrane fuel cell (PEM) or an alkaline fuel cell or stored as a metal hydride). The fuel cells that need no gas purifier, such as phosphoric acid fuel cells, are the heaviest and largest. A fuel cell that is relatively light-weight and compact, e.g. a PEM or alkaline fuel cell, generally needs complicated, delicate and expensive purifying apparatus to utilize hydrogen.
For cost and availability reasons, if the fuel is natural gas, then storage on vehicles such as fork lift trucks, automobiles, etc. is heavy, bulky, and of somewhat marginal safety. Gaseous hydrogen storage in such an environment is also a problem. It is either too voluminous (at low pressure) or too heavy (because of the tank or cylinder needed at high pressure). Moreover, both storage systems are potentially unsafe because of the combustibility of the hydrogen.
Storage of hydrogen as a metal hydride is also expensive since metal alloys suitable for hydrogen storage in readily reversible metal hydrides are expensive to fabricate and because they require the hydrogen to be free of carbon monoxide, carbon dioxide, and water vapor. Regeneration of such metal hydrides is also a problem because it requires pure hydrogen, which is relatively more costly than reformed natural gas, which is relatively inexpensive and contains impurities such as carbon dioxide and steam. Adding to the regeneration expense is the continuous supply of external cooling that is needed to drive the regeneration reaction. Recently it has been suggested that hydrogen be stored as H.sub.2 SO.sub.4 and reacted with scrap iron to produce hydrogen. Dandapani et al., Int. J. Hydrogen Energy, 11 (2), 101-105, 1986. This approach, however, is extremely costly because of the cost and weight of sulfuric acid. The weight of the stored acid also restricts its use.
The reaction of iron with water (steam) to produce iron oxide and hydrogen is well known. However, the conversion rate of the reaction is extremely low unless the water has been heated to extremely high temperatures and this results in a low overall efficiency and thus it has no current practical commercial utility. One attempt at creating a hydrogen generating system based upon the reaction is disclosed in U.S. Pat. No. 4,547,356 (Papineau) which suggests that hydrogen may be generated by the catalytic decomposition of steam at temperatures of 1,000.degree.-2,000.degree. F. (540.degree.-1,094.degree. C.) to form hydrogen and supposedly oxygen. The patent contends that at those temperatures, the steam will disassociate in the presence of "a catalyst of a web-like cellular structure defined by interconnected metal filaments comprising iron, copper, silver, nickel, palladium, platinum, or iron-nickel and molybdenum" and that the hydrogen can then be separated from the oxygen with a diffusion-based separation membrane, e.g. palladium. Water or steam is thermodynamically incapable of decomposing into hydrogen and oxygen within the stated temperatures. The patent asserts that more hydrogen will be produced by the process than will be required for reactivating the catalyst when it has become deactivated because of use. As such, the patent teaches a perpetual motion machine.
However, due to the low cost of iron, the desire to develop a hydrogen generating system based on the iron-water reaction which system will generate hydrogen at a commercially viable high rate continues. The present invention arose from such a desire and has increased the rate of hydrogen generation of the system of U.S. Pat. No. 4,547,356 from an average of less than 0.2% per minute for the first hour at 450.degree. C. (which dropped to 0.027% per minute for the second hour) to more than 2% per minute, thereby increasing the potential peak power by more than a factor of 10.
Accordingly, it is an object of the present to develop a process and system for more rapidly generating hydrogen in situ safely and at low cost.
It is another object of the present invention to develop an energy source which has a longer life than conventional storage batteries, need not be electrically recharged, and is an order of magnitude lighter in weight per unit energy produced.
It is a still further object of the present invention to develop a hydrogen generating system which is easy and relatively inexpensive to regenerate.
It is a still further object of the present invention to develop an energy source which is less delicate and less expensive than a metal hydride based hydrogen system.